Extraocular motoneurons comprise the final common output pathway for all ocular behaviors, typically categorized as saccades, smooth pursuit, vergence, and the vestibuloocular (VOR) and optokinetic (OKR) reflexes. Although motoneuron activity during these behaviors has been examined in detail, the bulk of unit study has been limited to extracellular recording. The goal of the proposed research is to obtain high-resolution intracellular records of subthreshold and spike events in extraocular motor neurons that will shed further light on details of their organization. This work will use a novel in vitro preparation developed by the sponsor's laboratory consisting of the isolated turtle brainstem with attached eyes and semicircular canals. This preparation provides the stability and control necessary for whole cell patch recording, yet permits the use of natural visual and vestibular stimulation. Aim 1 of the proposal is to investigate organization of the synaptic drive imposed on the extraocular motoneuron pool by different ocular behaviors. Specifically, responses recorded during fictive VOR, OKR, and saccades will be compared to identify how synaptic input from the different systems converges on individual motoneurons, whether functional cell groups exists within the extraocular motoneuron pool, and how the observed physiological responses correlate with morphology obtained from cell filling. Aim 2 of this proposal will examine general issues of motoneuron physiology in these neurons. This exploits the ability to simultaneously record population responses (from the cranial nerve) during intracellular recording, and will permit the investigation of recruitment order, spike failure rates, and the functional role of gap junctions within an extraocular motor nucleus.